1. Field of the Invention
The present invention relates to static type semiconductor memory devices, and more particularly to a static type semiconductor memory device which includes a spare column to replace a defective column.
2. Description of the Background Art
In an SRAM which has a bit line and a line of a ground potential GND that are formed of the same interconnection layer, an extraneous object or defocusing brought about by the process of interconnection formation may short-circuit the bit line and the ground potential GND line. Since the bit line which is short-circuited with the ground potential GND line is fixed to a low level, a defective column which includes such a bit line cannot perform correct writing and reading operations.
Conventional SRAMs have been improved in the yield of chips by replacing such defective columns with normal spare columns.
However, even if such a defective column is replaced by a spare column, the conventional SRAM continues to flow current from a line of a power supply potential VCC through a bit line load and a defective bit line to a line of a ground potential GND, and increases current consumption.
Especially, recent lower power consumption type SRAMs excessively increase standby current even if a defective column as described above is replaced by a spare column, and thus the SRAMs become defective.